As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
An information handling system may include one or more circuit boards operable to mechanically support and electrically couple electronic components making up the information handling system. For example, circuit boards may be used as part of motherboards, memories, storage devices, storage device controllers, peripherals, peripheral cards, network interface cards, and/or other electronic components. As is known in the art, a circuit board may comprise a plurality of conductive layers separated and supported by layers of insulating material laminated together, with conductive traces disposed on and/or in any of such conductive layers. As also known in the art, connectivity between conductive traces disposed on and/or in various layers of a circuit board may be provided by conductive vias.
Typically, during manufacturing of a circuit board, each via is formed to approximately the thickness of the circuit board, thus permitting electrical conductivity between traces on the various layers of the circuit board. As a result, a portion of a via may be “unused” in the sense that such portion is present but not needed to conduct a signal between circuit board layers. FIG. 1 depicts a circuit board 10 having a via 6 with an unused portion 8. As shown in FIG. 1, a circuit board 10 may include various layers, including ground planes 2 and signal layers having traces 4 formed therein. Pads 12 formed of substantially conductive material may also be formed in circuit board 10 in order to electrically couple traces 4 to vias 6 as desired. Thus, as can be seen from FIG. 1, a via 6 may have a portion used to create an electrically conductive pathway between traces 4 on different layers of circuit board 10, an unused portion or “stub” 8 which is not part of an electrically conductive path between traces 4.
A via stub 8 may act as an antenna, and thus may resonate at frequencies (and harmonics thereof) for which the length of via stub 8 is equal to one-quarter of the wavelength of such frequencies. As transmission frequencies used in circuit boards increase, signals operating at such frequencies may be affected by such resonances, resulting in decreased signal integrity.
Although various traditional approaches may be employed to mitigate the effect of via stub resonances, such approaches have disadvantages. For example, backdrilling or counter boring may be used in which a mechanical drill is used to remove a part of a via stub 8. However, such process may significantly increase the cost of circuit board manufacture. In addition, due to mechanical tolerances of a drill used to backdrill or counter bore, a small portion of via stub 8 may still remain, and thus some resonance may still occur.